arXiv Machine Learning

IR-PRM+ with Previous-Utility Prediction: Constant Regret and Best-Iterate Convergence

arXiv Statistics ML
Oct 2

Block Optimism for Nonstationary Bandits with Latent Linear Dynamics

The paper introduces a new algorithm for a nonstationary bandit setting where actions influence both immediate rewards and the evolution of an unobserved latent linear state. By approximating the infinite‑memory reward process with a finite‑memory block‑level proxy and applying a UCB‑based block algorithm, the authors achieve a regret bound of “~O(√T)”, improving upon the previous “~O(T^{2/3})” guarantee. This represents the first such “~O(√T)” result for latent linear‑dynamics bandits with bilinear rewards and an open‑loop action‑sequence benchmark.

By Taehyun Hwang, Hyunjun Choi, Heesang Ann, Min-hwan Oh
arXiv Machine Learning
Oct 16

Follow the Perturbed Leader for Linear Bandits: $\sqrt{T}$ Regret over General Convex Sets

The paper presents the first adversarial linear bandit algorithm based on Follow-the-Perturbed-Leader (FTPL) that achieves √T regret over general convex action sets. It achieves a regret of ≥O(d^{5/4}√T) using only linear optimization oracles, and a near‑optimal ≥O(d√T) regret when an optimal‑design exploration distribution is available. The work improves on previous FTPL algorithms and generalizes earlier results for special action sets, offering a simpler and more computationally efficient approach that relies on adaptive perturbation distributions and a new analysis framework based on Fisher information.

By Chen-Yu Wei
arXiv Machine Learning
Sep 4

Constant regret in general games via higher-order optimism

The paper presents an uncoupled learning algorithm, higher-order optimism with discounting (HOOD), for arbitrary N-player normal form games with up to K actions per player. HOOD achieves an individual regret bound of O(N³ log² K) uniformly over the play horizon by combining a discounted (N+1)-th order predictor with entropic regularization over a lifted strategy space. This design mitigates large oscillations in play, addressing a key challenge in prior attempts to attain constant regret in general games.

By Omar Abbadi, Rida Laraki, Panayotis Mertikopoulos
arXiv Machine Learning
Oct 19

Follow the Perturbed Leader for Linear Bandits: $\sqrt{T}$ Regret over General Action Sets

The paper presents the first adversarial linear bandit algorithm based on Follow-the-Perturbed-Leader (FTPL) that achieves √T regret over general action sets. It attains a ≥O(d^{5/4}√T) regret using only linear optimization oracles, and a near‑optimal ≥O(d√T) regret when an optimal‑design exploration distribution is available. The authors introduce adaptive perturbation distributions—including Gaussian, random‑weighting, and elliptical perturbations—and develop a systematic analysis of the FTPL stability term via Fisher information, extending the FTPL framework beyond previous approaches.

By Chen-Yu Wei
arXiv Machine Learning
Oct 22

The Price of Current-Effect Inference in Nonstationary Multi-Armed Bandits

The paper studies the trade‑off between maximizing rewards and accurately estimating current treatment effects in nonstationary multi‑armed bandits. For $K$‑armed bandits with H"older‑smooth mean rewards, the authors derive minimax bounds on expected dynamic regret under a high‑probability simultaneous coverage requirement for all current effects. They propose the TRACE algorithm, which achieves a regret–precision trade‑off that separates reward‑learning regret from the unavoidable cost of refreshing current‑effect estimates, and extend the method with an empirical‑Bernstein e‑process to adapt exploration while preserving worst‑case guarantees.

By Sharan Sahu, Martin T. Wells